This invention relates to an improved electrostatic recording material having a dielectric recording layer formed on a surface of a base sheet and an improved method for the production of the same.
The electrostatic recording system has recently been widely applied to a facsimile or a computer input-output system or the like as a system suitable for high speed recording in a speed telecommunication system, a high speed graphic reproduction system, etc. The electrostatic recording material as a recording medium basically comprises a highly dielectric film layer, which serves as an electric-charge-retentive layer, and a base sheet of lower resistance, which supports the film layer. The dielectric layer of the electrostatic recording material comprises an insulating polymeric material. For example, the dielectric layer is produced by applying to a base sheet a coating composition prepared by dissolving polystyrene, polyacrylate, polyvinylidene chloride, polyvinyl acetate, polyacetal, nitrocellulose or silicone resin in an organic solvent such as acetone, toluene, benzene or methyl ethyl ketone, or a coating composition comprising an emulsion of a copolymer of vinyl acetate with acrylic ester, a copolymer of vinyl acetate with methacrylic ester, a copolymer of vinylacetate with styrene or a copolymer of vinyl acetate with crotonic acid.
Electrostatic images of an electrical signal formed on the electric-charge-retention layer are made visible by a toner which has a polarity opposite to the polarity of the electrostatic image charge, and brought into permanent visible images by further fixing treatment. The electrostatic recording process usually involves electric discharge between a voltage applying electrode and the electric-charge-retentive layer. In order to carry out an effective and uniform electrification with a relatively low discharge voltage it is desired to make the surface of the electric-charge-retentive layer relatively rough unless it produces any white spots in the recorded images or it lowers distinctiveness of the recorded images. Such a surface condition of the electric-charge-retentive layer as this is particularly required for an electrostatic recording system having a high resolving power and a high recording speed.
It is conventional to add pigment powder to an insulating resin coating composition for forming a dielectric layer to make the surface of the dielectric layer rough, whereby a mat finished surface having an improved writability is obtained. Heretofore it has been inevitable that addition of such pigment powder causes a decrease in the electric resistance of the dielectric layer formed, deterioration of electrostatic characteristics such as charge acceptance and charge decay and lack of moisture resistance.
The primary object of the invention is to provide an improved electrostatic recording material having a finely roughened dielectric layer surface on which clear images can be recorded.
Another object of the invention is to provide an improved electrostatic recording material having a mat-finished appearance similar to that of commonly used business papers.
A further object of the invention is to provide an improved electrostatic recording material having a good receptivity and a good retentivity for writing and marking.
Other objects and advantages of the invention will become apparent from the following description.